Polar vortex, polar pig and other weird ways to describe this weather

Why don't we just say it's bitterly cold? We could, but where's the fun in that?

Why does Chicago feel like the Arctic today? It's because of the polar vortex.

Oh, ok. Wait, what is the polar vortex? While there's a lot of meteorological science behind it, it's actually pretty easy to explain.

According to the website climatecentral.org, during the winter months there's a high altitude, cold low pressure area that normally spins around the North Pole. But it's not just any low pressure - it's a hurricane-like system with winds that can reach or exceed 100 mph. It's that low pressure area that plays a big role in determining how cold things get south of there, from southern Canada and into the United States and beyond. Now imagine that low pressure being a giant refrigerator. When things are normal and the polar vortex is strong, the refrigerator door is tightly sealed and the cold air stays inside.

But if the polar vortex weakens or is otherwise interrupted - imagine a spinning top that loses its momentum - the refrigerator door opens and allows cold air to spill into areas that may not be accustomed to such extremes.

Under normal conditions, the polar vortex is strong. That creates relatively mild weather in the U.S., Europe and Asia. But when it's weak and the air is allowed to escape, cold air infiltrates those same areas. In this particular case, the polar vortex has not only been disturbed but it's strong enough to bring some of the coldest weather the Chicago area has seen in 20 years.

Some websites, namely Bloomberg.com, have chosen to refer to the polar vortex as a "polar pig," apparently because the system takes on a pig-like shape on weather maps. (Editor's note: Please do not call it that). More common is the term "Siberian Express," which is a meteorological term in the U.S. for cold air of Arctic origin. Chicagoans using the popular hashtag #chiberia to describe this event may find it interesting that air in a Siberian Express pattern doesn't necessarily originate in Siberia.

So when your mother told you not to leave the refrigerator door open while deciding what to eat, she may have been on to something bigger.